Genetic testing

DNA testing, also known as genetic fingerprinting, DNA typing, and DNA profiling, refers to a suite of techniques employed to distinguish between individuals of the same species using only DNA samples. It has become a revolutionary tool in both forensic science and biological research since its introduction in 1985 by Sir Alec Jeffreys at the University of Leicester.

CBP chemist reads a DNA profile.jpg

Overview

DNA testing is predicated on the fact that while two humans share a vast majority of their DNA sequences, certain regions, known as minisatellites, are highly variable. These repeating sequences can be analyzed to establish a genetic profile so unique that it's unlikely to have arisen coincidentally, with the exception of identical twins.

Historical Development

The invention of DNA testing by Sir Alec Jeffreys ushered in a new era for biological and forensic sciences. Genetic fingerprinting capitalizes on the differences in minisatellite sequences among individuals. Two unrelated humans would typically exhibit different numbers of minisatellites at a given location on their DNA.

PCR Detection

Through the use of polymerase chain reaction (PCR), it's possible to detect the number of minisatellite repeats at various loci. This has drastically enhanced the specificity and accuracy of DNA testing.

Applications

Forensic Science

One of the primary applications of DNA testing is in the realm of forensic science. It has been instrumental in matching suspects to biological samples such as blood, saliva, or semen found at crime scenes. Furthermore, DNA testing has facilitated the exoneration of many individuals previously wrongly convicted.

Other Applications

• Identifying Human Remains: Helps in the identification process of decomposed or fragmented remains.
• Paternity Testing: Assists in establishing biological parentage.
• Organ Transplantation: Matches organ donors with recipients.
• Wildlife Studies: Assists in the tracking and study of animal populations.
• Food Provenance: Determines the origin and composition of food items.
• Historical Migrations: Forms hypotheses about human migrations in prehistoric times.

Legal Aspects

The execution of DNA tests is governed by the legal codes of individual jurisdictions. While most tests are voluntary, certain situations, like a court order or search warrant, can mandate them. Numerous jurisdictions have begun assembling databases with DNA information from convicted criminals.

Techniques

DNA Extraction

The process begins by extracting DNA from cellular samples which might include blood, saliva, semen, or other relevant tissues. Buccal swabs are commonly utilized for collecting reference samples.

RFLP Analysis

Initially, DNA fingerprinting hinged on restriction fragment length polymorphism (RFLP) analysis. This technique, although foundational, has largely been superseded by newer methodologies. RFLP was notably critiqued for being time-consuming and requiring sizeable DNA samples, often of high quality. This made it less feasible for analyzing compromised samples.

PCR Analysis

The advent of polymerase chain reaction (PCR) marked a pivotal moment in the evolution of DNA fingerprinting. PCR techniques demand smaller DNA samples, which can also be more degraded than those required for RFLP.

AmpFLP

The AmpFLP technique, developed in the early 1990s, was faster than RFLP and utilized PCR to amplify DNA samples. It primarily relied on variable number tandem repeat (VNTR) polymorphisms. AmpFLP remains popular in lower-income countries due to its cost-effectiveness and operational simplicity.

STR Analysis

Currently, short tandem repeats (STR) based methods dominate DNA fingerprinting. STR techniques, which use highly polymorphic regions with short repeated DNA sequences, have become the standard due to their accuracy and reliability.

Limitations and Concerns

It's worth noting that while DNA testing is a powerful tool, it's not without limitations. For instance, samples from identical twins will produce identical genetic profiles. Moreover, testing methods like RFLP can be labor-intensive and may not yield reliable results with degraded samples.

See Also

• Minisatellites
• Polymerase Chain Reaction (PCR)
• Forensic Science
• Genetics